'I used to be the most shambolic person...'

Historian Simon Sebag Montefiore talks to Elizabeth Grice about his obsession with Stalin, his colourful past and how marriage saved him

Simon Sebag Montefiore's young son, Sasha, knows what it feels like to live with a dictator. When his dad came down to breakfast the other day, the four-year-old chirped up: "Morning, Young Stalin!" Like the rest of us, he is finding his father's obsession difficult to ignore.

Between recommendations for hair loss treatments, vasectomies and the musical Spamalot, Stalin's sinister portrait is currently hogging five consecutive escalator advert boards on the London Tube.

"Child. Man. Monster. Find out How it Happened." Sebag Montefiore's new book, Young Stalin, is being plugged as the intellectual's beach read this summer, a ground-breaking work of thrilling energy and scholastic thoroughness that has turned up a wealth of new material on the early sexual, political and criminal career of Josef Stalin - never mind that it will break most people's baggage weight allowance.

Sebag, as he is generally known, is all nervous excitement - while his family are simply relieved to be out of the shadow of a murderous tyrant.

"I am ashamed to say that both my children knew Stalin before they knew Thomas the Tank Engine," he admits. His wife, Santa, a prolific writer of romantic novels, found the blood-soaked presence of Stalin in their marriage a trial of endurance but, in a touching coda to five pages of acknowledgements, he praises her endlessly "sunny encouragement and serene charm".

All of them, he says, are now thankfully entering their own period of deStalinisation.

Santa and Sebag, a cottage industry of literary productivity, sound like characters in a novel themselves.

He, a buccaneering sort of adventurer-turned-historian, youngest of four sons, his doctor father a Lithuanian Jew, his mother from Poland, not a drop of English blood in his veins.

She, the daughter of an old English farming family, the Palmer-Tomkinsons, friends of the Prince of Wales, perennial source of gossip column interest.

By the time they met, he had several lives behind him - failed investment banker, novelist, self-appointed war reporter, journalist. His best man, journalist Robert Hardman, memorably described him at their wedding as a cross between Woody Allen and Biggles.

Although he was starting to reinvent himself as the historian he'd always wanted to be, based on his knowledge of Russian affairs, it was a haphazard stab at being the homme serieux. Then, a friend told him about this amazing girl who worked in a perfume shop on Walton Street...

"Before Santa, I used to be the most shambolic person. I was all over the place, trying to do too many things, dating about 10 girls at the same time, travelling chaotically and missing aeroplanes, never settling down to anything, failing to meet deadlines. I was a complete mess.

"She grounded me. I have become very disciplined now. I would never have written the books without her. Definitely the cleverest thing I ever did was to marry Santa. Maybe it's the only clever thing I did."

But all along, the Santa effect notwithstanding, there seems to have been method in Sebag's singular disarray. He says he was a vile youth, but there was a cunning charm that meant he could blag his way into anything, untroubled by any sense of self-doubt.

At 10, he wrote his first novel - My Affair with Stalin. At 17, he talked his way into Downing Street to interview Margaret Thatcher for his school magazine, The Harrovian.

Unintimidated by being told not to slouch and to pull his socks up, he plagued the prime minister with cheeky questions. Fellow Cambridge undergraduates would return from their summer travels with tales of lost temples to find that Sebag had inveigled himself into the White House and snaffled an interview with Caspar Weinberger, Ronald Reagan's defence secretary.

After Cambridge (where he read history but is said never to have found the library), his contemporaries were joining the stampede to the City but Sebag went one better, posing as a New York investment banker.

"He was pretty b----- useless," recalls a friend, "but he talked a good talk, wore the clothes and would sit with his foot on the chairman's desk." That phase lasted for five years. Koo Stark and Tatler girl about town, Nicola Formby, were among his girlfriends.

Then the Soviet Union broke up and Sebag seized the moment for a picaresque adventure to Tbilisi, Samarkand and Baku. "All my life I had wanted to do this. I had to go."

Everywhere he went, like some reincarnation of William Boot in Evelyn Waugh's Scoop, he seemed to find himself in the middle of a revolution, the only man able to file an on-the-spot story because "proper" journalists were all in Moscow.

When civil war broke out, he was in Tbilisi and demanded: "Take me to your president." From the presidential desk, which had the only working phone, he rang his mother to reassure her he was all right - while the dictator was on his balcony, addressing a Kalashnikov-waving mob.

He pitched up in Groszny just before the Russian invasion. In Estonia, he was approached by the royalist party, asking him if he would offer the Estonian throne to Prince Edward.

"It was the Ruritanian mission I had dreamed of. It was treated as a jokey news story, but I think it was a missed opportunity."

Twice, he came close to being killed in Boy's Own escapades in bandit republics and it sobered him up. "In these war places," he says, "you fall into the hands of terrified, terrifying young people with guns who are likely to kill you out of panic or carelessness or wanton caprice, without ever knowing who you were.

" That is what is depressing: the randomness of death. You realise it is not worth it and you should really come home."

Domestic journalism was never going to offer the same thrill as mixing with warlords, though, and things reached a nadir when he was sent to interview the weather girl Sian Lloyd: it was time to get serious.

Using the web of contacts he had made in Russia, he started researching his life of Catherine the Great and her lover, Potemkin. Its success opened unexplored archives to him for his next opus: Stalin: The Court of the Red Tsar.

"A signal went out from the Kremlin that I was to have access." By the time he embarked on the prequel, Young Stalin, he had located a treasure trove of unpublished material, particularly in Georgia, including Stalin's love-letter postcards to women, critical memoirs by members of his family (for which they were shot) and a well-buried memoir written by his mother.

"I was pretty thrilled. As far as I can tell, Stalin never knew she had done this. He was absolutely insistent that there were to be no Hello-style interviews with her."

Discovering that Stalin was a psychopath, arch-seducer and criminal from an early age, masterminding bank robberies, protection rackets, arson, piracy and murder, suited Sebag's taste for the macabre. "I love the flamboyance, the melodrama, the bloody theatre of Russian history."

There's no let-up in his evangelistic zeal to make history exciting and approachable. In September, he publishes 101 Heroes: Great Men and Women for an Unheroic Age, followed by Jerusalem: The Biography, and then another sanguinary tale, The Romanovs: The Intimate Chronicles of the Russian Imperial Family.

Somewhere in between, there'll be his novel - a multi-generational saga about a Jewish family, including Stalin, Rasputin and the oligarchs.

At least the Montefiores aren't still writing at opposite ends of their dining-room table.

This was how they worked when they lived in Battersea and it led to frequent arguments about their choice of background music - should it be "mawkish nonsense like Celine Dion [Santa's choice]" or his superior preference for Guns N' Roses, Leonard Cohen and David Bowie?

"Santa wrote four novels while I was writing Catherine and Potemkin at the same table. It is amazing that our marriage survived."

It all started when a suitor who'd failed to make any headway with Santa Palmer-Tomkinson, now 37, recommended her to Sebag. "The way he described her, I thought she sounded so romantic and pure and wholesome and unusual."

On their first date, over tea, they found they both knew Evita by heart and ended up singing it from beginning to end, he dressed up in a greatcoat as General Peron, she playing Evita.

He says he fell in love with her when she played the piano. "Till then, my love life had been pretty messy. I wasn't sure I was cut out for marriage. Then I realised Santa was the first person I'd ever met who I could contemplate being married to.

" That was a big thing. Then I realised I was in love with her. Then I realised that if I didn't marry her she might leave. When she converted to Judaism for me, that was more than a marriage. The ultimate expression of love."

They were married at the Liberal Jewish Synagogue in St John's Wood in 1998 and Prince Charles and Camilla Parker Bowles, great friends of the Palmer-Tomkinsons, chose the occasion for their first public outing together.

Recently, the Montefiores hosted a dinner party at their home in Kensington where Charles and Camilla met their mutual friends, David and Samantha Cameron, allegedly to talk about green issues.

"People used to ask me what it was like moving into that family [Santa's more wayward and eccentric sister is Tara P-T]. They were very unusual people from the beginning. They were amazingly supportive about Santa becoming Jewish and that is pretty exceptional for a British country family.

" They are an entertaining, colourful family and I like that. My family is fairly eccentric, too, so it's like living in a madhouse, but fun."

Sebag, 41, claims he has a hermetical, workaholic streak. During his second big Russian book, he fell ill with fatigue. After a decade of no exercise beyond wandering round bookshops, he's taken up boxing to work off his frustrations with reviewers and publishers.

"When I'm up, I'm over-exuberant; when I'm down, I just wander round on my own. I have no middle space. Santa always knew I would travel a lot and probably finds it a relief to have me out of the house. I am much better-tempered when I travel."

Since the birth of their two children, Lily, aged six and Sasha, four, Sebag has limited his foreign travel to two weeks at a stretch.

"I miss them, so I get home more quickly now. They are my greatest joy. Because I work at home, I probably see more of my children than anyone else I know.

" They come up and see me all the time. If I'm on a real write-athon, I'll go downstairs and kiss them on the forehead, bound back up again and keep going. That's heaven, isn't it?"

•Young Stalin by Simon Sebag-Montefiore (Orion) is available for £23 + £1.25 p&p. To order please call Telegraph Books on 0870 428 4112 or visit books.telegraph.co.uk